The overall goal of this project is to identify cellular and molecular triggers that promote heart failure (HF) and to determine novel molecular-targeted therapeutic strategies to treat them. The central hypothesis is that HF can be caused by disruption of molecular signaling complexes and processes that, in normal hearts, underlie balanced regulation of cellular activity and that altered cellular calcium (Ca2+) homeostasis plays a critical role in HF progression. This project focuses on elucidating defects in the regulation of type 2 ryanodine receptor (RyR2)/Ca2+ release channel, which is required for cardiac excitation-contraction (EC) coupling. In the previous period of this project the PI showed that a diastolic SR Ca2+ leak via defective RyR2 can contribute to SR Ca depletion and impaired contractility in HF. The PI identified a defect in RyR2 in patients with HF: leaky PKA hyperphosphorylated and oxidized RyR2 channels that exhibit decreased binding affinity for the stabilizing subunit calstabin2 (FKBP12.6). This observation has directly lead to the development of a novel potential therapy for HF, RyCal (S36, which is a JTV-519 derivative without HERG and L-type channel blocking activities), representing a new class of intracellular calcium channel stabilizers that improve cardiac function in murine and canine HF models and are now in Phase II trials in patients with class II and III HF. The PI showed that the phosphodiesterase PDE4D3 is a component of the RyR2 complex and is protective against HF because mice that are deficient in PDE4D3 are predisposed to HF following MI. Moreover, oxidation of RyR2 depletes the channel of PDE4D3 and calstabin2 rendering the channel leaky and promoting HF progression. The PI proposes to test the hypothesis of a vicious cycle between RyR2 and mitochondria due to Ca2+ leak via RyR2 that poisons mitochondria resutling in increased ROS prodcution which further oxidizes RyR2 and exacerbates the leak. Two aims are proposed: 1) determine whether RyR2 mediated intracellular Ca2+ leak causes mitcondrial dysfunction in HF using RyR2-S2808D mice with constitutively leaky RyR2 channels; and 2) determine whether mitochondrial ROS are responsible for depletion of the RyR2 complex of calstabin2 and PDE4D3 and whether targeting of catalase to mitochondria reduces RyR2-mediated Ca2+ leak and protects against HF progression in the post-MI model. The proposed studies are significant because they will provide novel insights concerning the mechanisms of HF progression.